Microchannel plates

Abstract

Microchannel plates (MCPs) are compact electron multipliers of high gain. They have been used in a wider range of particle and photon detection systems perhaps more than any other kind of detector. A typical MCP consists of about 10,000,000 closely packed channels of common diameter which are formed by drawing, etching, or firing in hydrogen, a lead glass matrix. Typically, the diameter of each channel is ~ 10 microns. Each channel acts as an independent, continuous dinode photomultiplier. In astronomy, and in the many other fields that use MCPs, the detectors are generally used for distortionless imaging with very high spatial resolution. Physical principles of MCP operation The fundamental physical principals of MCP detectors are gain, efficiency, energy resolution, spatial resolution, time resolution, and dark noise. X-rays interact with the channel plate glass and electrodes (and with the associated photocathode material) via the photoelectric effect. For X-ray energies below about 5 keV, detection proceeds in a 'single channel mode'. That is, no significant fraction of the X-ray beam entering a given channel penetrates the channel wall to illuminate the neighboring channels. At higher energies, this 'channel crossing' phenomena becomes important. Another important property of MCPs is their relative immunity to magnetic fields. A single plate with typical operating parameters is completely unaffected by being immersed in a 0.5 Tesla magnetic field. Stacks of plates in certain orientations are immune to much higher fields. This property has only just begun to be exploited in the space astronomy world.

A low background-rate detector for ions in the 5 to 50 keV energy range to be used for radioisotope dating with a small cyclotron

“…A micrometer-driven mechanical feedthrough allowed us to move the slit in the 0.8 mm direction. We used an oven-type 23 Na + ion source. The unpurified sodium in the source also provided us with isotopes of the heavier alkali metals.…”

“…In the mass spectrometer we tested the detector with positive ion beams of 12 C, 23 Na, We measured the effect of ion incidence angle, species, and velocity on mean secondary-electron yield. To find the mean yield we divided the integrated output current by the ion count rate and the electronic charge.…”

Optimization of the performance of a tandem microchannel plate detector as a function of interplate spacing and voltage

“…In this time the average electron will move out to a radius (2) , m ~ so the width of the electron cloud hitting the second Mep will be LV 1 / 2…”

Atom probe field ion microscope study of the range and diffusivity of helium in tungsten

“…No evidence presently exists demonstrating a proportionality between pulse height and number of incident ions. In fact considerable evidence does exist (15,80) which indicates a very broad pulse-height distribution resulting from a single incident ion. This strongly suggests that establishing an accurate and useful proportionality between number of incident ions and detector pulse height would be extremely difficult.…”